1. Field of the Invention
The present invention relates generally to centrifugal compressors, such as a centrifugal supercharger for providing increased airflow to an engine. More particularly, the present invention concerns an improved transmission lubrication arrangement for effectively lubricating the transmission components that drivingly connect the impeller to the power source, without having to tap into the lubrication system for the engine and without limiting the transmission speed.
2. Discussion of Prior Art
Centrifugal superchargers are traditionally provided with an internal step-up transmission that serves to rotate the impeller significantly faster than the input shaft connected to the engine. It is particularly known to provide a centrifugal supercharger with an internal belt drive supported by prelubricated (e.g., grease-packed) bearing assemblies. Although this type of transmission eliminates the need for lubrication (except for that already provided with respect to the bearing assemblies), it is believed to have relatively low operational limitations that effectively prohibit the supercharger from generating large amounts of pressure increase and airflow. On the other hand, a number of conventional centrifugal superchargers, particularly the higher boost models, utilize a gear drive that must, along with the bearing assemblies supporting the gear drive, be continuously lubricated during operation. Those ordinarily skilled in the art will appreciate that gear-type transmissions generally have greater structural integrity and are able to transfer significantly more load than a belt-type transmission. However, a gear-type transmission typically requires dispersion of lubrication fluid generally throughout the transmission chamber.
In the past, such a lubrication requirement has been problematic. First, lubrication fluid is commonly supplied to the transmission chamber of the supercharger from the engine. This almost always requires a fluid line to be tapped into the oil reservoir of the engine, which is often considered highly undesirable. It might be possible to alternatively provide a separate lubrication reservoir dedicated solely to the supercharger, although such a circulating arrangement would obviously be costly and consume a considerable amount of valuable engine compartment space. With respect to either alternative, the manner in which lubrication fluid is typically directed to the transmission components (e.g, jets, wicking arrangements, etc.) is believed to be unreliable, ineffective and/or in other ways problematic.
Although a circulating arrangement for the lubrication system would be costly and space consuming as indicated above, there are some advantages to such a system. For example, the lubricant can be filtered and cooled externally to the supercharger prior to reentry. However, prior art recirculating systems suffer from the undesirable risks associated with tapping into the engine's lubrication system. Furthermore, the prior art recirculating systems are prone to flood, or excessively lubricate the transmission and are undesirably subject to the lubricant draining out of the transmission under certain conditions.
There are also “self-contained” friction ball driven (e.g., Bendix drive) superchargers. That is to say, a number of superchargers wholly contain the lubrication fluid therein. Those ordinarily skilled in the art will appreciate that the transmission chamber of such a supercharger is typically filled with lubrication fluid. It has been determined, however, that a fluid-filled transmission chamber actually reduces the load capacity of the supercharger, as a result of the significant hydraulic separation forces caused by flooding the transmission and bearing assemblies. Furthermore, this type of construction adds heat and fails to provide sufficient cooling of the transmission.